Turbulence and Geophysical Flows

The dynamics of turbulent flows remains an outstanding challenge of out-of equilibrium physics with important implications for industrial and natural settings. The research carried out at SPHYNX aims to characterize the energy pathways of such turbulent flows from the large injection scale to the tiny erratic dissipative structures.

Focusing on flows driven by thermal convection, we have obtained an unambiguous observation of the ‘ultimate regime’ of thermal convection, at play in geophysical and astrophysical flows . In the ocean and atmosphere, the latitudinal temperature gradient between the equator and the poles also induces a strongly turbulent flow. We have developed a theory for the associated turbulent transport based on the study of idealized models of increasing complexity . Such large-scale properties of turbulent flows are intimately connected to the way the flow dissipates energy at small scale: turbulence induces intense dissipative structures at very small scale that remain out of reach to most experimental studies.

We have thus designed a ‘Giant Von Karman’ laboratory experiment, which provides a unique opportunity for the detailed spatio-temporal characterization of the small-scale intermittent dissipative structures of the flow , in connection with possible singularities of the Euler and Navier-Stokes equations. To access dissipative structures, we are developing two types of optical metrology methods : We designed an innovative Diffusive-Wave Spectroscopy method that allows for the direct spatio-temporal measurement of the turbulent dissipation rate at a solid wall . We are also developing new post-processing algorithms for Particle Image Velocimetry to measure extremely dense 3D time-resolved Lagrangian, Eulerian and pressure fields.